An outdoor mobile communication environment and an indoor short-range communication environment are under very different conditions. Hence, different systems support communications in these environments. For example, Global System for Mobile telecommunication (GSM), Interim Standard-95 (IS-95), Wideband Code Division Multiple Access (WCDMA), and Code Division Multiple Access-2000 (CDMA-2000) were developed for outdoor communications, whereas Institute of Electrical and Electronics Engineers (IEEE) 802.11a, IEEE 802.11b, and Wireless Fidelity (WiFi) were developed for indoor communications.
Along with user demands for more various and more complex services, future-generation communication systems should be able to provide diverse services including voice and data simultaneously in an integrated fashion irrespective of place, indoor or outdoor. To meet those demands, the present separate communication systems for indoor use and outdoor use can be integrated into a single system, but with the following drawbacks.
(1) Interworking is complex and a processing delay occurs between the two systems. Although technologies such as Media Independent Handover (MIH) have been developed for vertical handover to solve the problems, they still require complex protocols and procedures.
(2) Since the two systems use different frequency bands, flexible frequency use is difficult. For instance, a WiFi system uses an unlicensed band and a legacy mobile communication uses a dedicated licensed band. Accordingly, it is difficult to use a licensed band for an indoor communication system.
(3) A user terminal should be equipped with a function of using the two systems. Therefore, the implementation complexity of the terminal increases.
As described above, the convergence between different systems aiming at integrated provisioning of different services including voice and data indoors or outdoors faces many problems. Accordingly, there exists a need for an effective technique for supporting cells with different characteristics in order to meet more diverse and more complex user demands.